During the manufacture of electron tubes the electrode assembly and tube envelope are heated to elevated temperatures in order to degas the internal components and surfaces. This degassing, or baking, takes place while the electron tube is being evacuated, or under pumping. After conversion and activation of the cathode of the electron tube it is sealed off from the pumping system and a getter device within the electron tube is activated to make it capable of sorbing the residual gases during the life of the electron tube. Some of these latter stages may however take place in a slightly different order.
It is known that the residual gas atmosphere during and after tube processing can later affect the properties of the tube.
It has been found that there can be a beneficial effect on tube life and performance if water vapor is introduced into the electron tube during its manufacture or processing. Kanellopoulos (U.S. Pat. No. 3,589,791) proposes the use of a sponge soaked in water, allowing atmospheric air drawn through the sponge to cause water vapor to enter a kinescope as it cools down after a fritsealing process. Such processes are tiresome, however, as they require the additional steps of placing and removing the sponge in the neck of the kinescope. Furthermore excess water often has to be removed. The sponge may become soiled with the risk of introducing extraneous material within the tube. If the sponge is discarded the process may become relatively costly. As the amount of water contained in the sponge is not easily controllable it does not produce a reproducible quantity of moisture within the electron tube.
Using a sponge also means that during the vacuum baking stage the moisture previously introduced may be completely removed during the initial part of the baking cycle which leads to less beneficial effects on the cathode during the final processing stages.
Another known method is by the use of calcium hydroxide in a rupturable container. However, calcium hydroxide has not proved altogether satisfactory. Furthermore, the use of a rupturable container is awkward.
Barium hydroxide and zirconium hydroxide have also been suggested.
It is therefore an object of the present invention to overcome one or more of the disadvantages of prior means of introducing water vapor into electron tubes.
Another object of the presente invention is to provide a water vapor releasing composition of matter and device capable of releasing water vapor during the processing of an electron tube.
A further object of the present invention is to provide a water vapor releasing composition of matter and device capable of releasing a first part of its water content during baking of the electron tube and a second part of its water content at temperatures higher than those encountered in tube bakeout.
Yet a further object of the present invention is to provide an improved method of processing an electron tube.